Continuation is proposed of an integrated program project whose purpose is to carry out basic behavioral studies in mental retardation and intellectual development, with a primary focus upon learning and its facilitation, and to try to identify areas in which basic concepts can be applied to the solution of practical problems that arise in the education, training, and habilitation of retarded children. The research program is cnducted in the Institute on Mental Retardation and Intellectual Development, and is organized into three interrelated laboratories (research groups): comparative development, symbolic processes, and intrinsic motivation. Among the specific problems to be investigated are the following: basic learning and developmental processes across a variety of species ranging from reptiles to primates, including studies of imprinting, contingent and noncontingent schedules of reinforcement, and effects of responsive versus nonresponsive environments on learning ability of young rhesus monkeys; studies of semantic priming effects at differing developmental levels; recognition processes in memory utilization in retarded and non-retarded children; developmental studies of linguistic comprehension; structure of personality and motivation in mentally retarded persons; exploratory and play behavior in the development of intrinsic motivation.